This invention relates to a display device having a thin-film three-layered EL structure and more particularly a method for driving the display device for assuring legibility of a visual display and reliability of long-term operation.
A thin-film EL display panel is constructed with an array of scan electrodes and an array of data electrodes crossing the scan electrodes in a direction normal thereto and a number of EL pixels lying sandwiched between a respective one of the data electrodes and a respective one of the scan electrodes. After scanning is completed throughout the panel by the sequential application of a write pulse V.sub.W to the scan electrodes in a line scanning fashion, a refresh pulse of an amplitude V.sub.R is applied to complete an alternating cycle of driving.
Whether or not respective pixels on the same scan electrode are excited is determined by pre-charging by a modulation voltage V.sub.M and especially with supplying the pixels desired to be excited with a write voltage of V.sub.W +V.sub.M and supplying those desired to be non-excited are supplied with a write voltage of V.sub.W -V.sub.M. This driving method is suggested by many patents which are assigned to the assignee of the present application, for example, U.S. Pat. No. 3,946,371 to K. Inazaki et al, U.S. Pat. No. 3,967,112 to Y. Kanatani et al, U.S. Pat. No. 4,024,389 to Y. Kanatani et al, U.S. Pat. No. 4,070,663 to Y. Kanatani et al, etc. These patents are hereby incorporated by reference into the specification of the present application. With those suggested driving methods, a so-called burning phenomenon takes place where a fixed display pattern of figures and characters remains when the display panel has displayed the fixed display pattern for a substantial period of time and an attempt is made to return the panel to its original or non-displayed state.